With the increasing size of large scale integrated circuit chips, the number of input and output connections that have to be made to a chip has correspondingly increased. This trend has encouraged the evolution from dual in-line chip packages, which have two parallel rows of connection pins, to smaller and more dense leadless chip carriers. Leadless chip carriers generally consist of a package containing a square plate of ceramic, such as alumina, which forms a chip carrier or base onto which a chip is mounted. The chip carrier is then surface mounted, usually onto a generally larger printed circuit (pc) board or other ceramic chip carriers, simply by placing the carrier on top of corresponding contact pads which mirror those contact pads of the chip carrier. An electrical and mechanical connection is then made by soldering the chip carrier to this generally larger board by reflow soldering. Electrical connection paths within the leadless chip carrier allow the pads of the chip to be brought to external contact pads formed around each of the four sides of the ceramic base of the carrier. One technique for providing the electrical connection path comprises wire bonding of the leads of the chip to the external contacts. During this process very thin wires may be manually or automatically placed between the chip pads and the chip carrier pads to provide the electrical connections. This arrangement is less cumbersome than mounting dual in-line packages onto a board and allows greater density of input and output connections to be achieved.
In order to eliminate the expense, and complexity of wire bonding process, a so called flip-chip technology was initiated. In this technology a bumped integrated circuit (bumped IC) which carries a pad arrangement on a major top surface is turned upside-down, i.e. flipped, allowing direct coupling between the pads and matching contacts on the main circuit board or the chip carrier. The direct connection is facilitated by growing solder or gold bumps formed on the IC input/output terminals. The flipped bumped IC is otherwise referred to as a flip-chip. The flip-chip is then aligned to the cip carrier and all connections are made simultaneously be reflowing the solder.
However, direct bonding of the flip-chip die to the chip carrier or the wire bonding process makes impossible the removal of the die for testing and/or repair purposes.